The present invention relates to a zeolite used suitably in hydrotreating heavy oil, in particular a modified zeolite having a distinctive pore size distribution.
In recent years, a world-wide tendency is that crude oil is becoming more and more heavy, and consequently the amounts of sulfurous and nitrogenous compounds, metallic compounds such as nickel, vanadium and the like and, further resinous matter including asphaltenes are increasing conspicuously. On the other hand, there is an increasing demand for light oil such as kerosene and gas oil including desulfurized oil, denitrogenized oil and demetalized oil, which is accompanied with serious problems that the heavy oil of inferior quality is abundant and on the other hand the light oil is in short supply.
In order to cope with the situation like this, a method of hydrotreating heavy oil with a zeolite-containing catalyst has been proposed and put to practical use. However, the pore diameter of the zeolite conventionally used in hydrotreating catalysts is almost about 10 .ANG.. Due to this, when hydrotreating the heavy oil containing high molecular weight compounds such as resinous materials including asphaltenes in large amounts, and further containing large amounts of sulfurous and nitrogenous compounds and metallic contaminants, by the use of the catalyst containing the zeolite of this sort, a satisfactory result can not be obtained because it is difficult to cause the high molecular weight compounds to enter the pores of the zeolite. Further, there was a defect that a large amount of low value gas was produced.
For the purpose of partly modifying a high crystalline zeolite or increasing the SiO.sub.2 /Al.sub.2 O.sub.3 ratio of zeolite, there is proposed a method of treating zeolite with acid in Japanese Patent Publication No. 21802/1976 and Japanese Laid Open Patent Application No. 101003/1978. And, Japanese Patent Publication No. 43782/1981 and Japanese Patent Publication No. 16925/1982 each discloses a method of treating zeolite with steam and thereafter with ammonia. However, these prior art discloses give no heed to the pore size distribution of zeolite. According to our finding, furthermore, these conventional zeolites have no pore size distribution as defined by the present invention and render no satisfactory results in the points of activity, coke deposition and duration of life in hydrotreating heavy oil.